U.S. patent application number 14/601714 was filed with the patent office on 2015-05-14 for method to increase corrosion resistance in ferritic nitrocarburized treated cast iron substrates.
The applicant listed for this patent is GM Global Technology Operations LLC. Invention is credited to Michael D. Hanna, Michael L. Holly.
Application Number | 20150129377 14/601714 |
Document ID | / |
Family ID | 43822268 |
Filed Date | 2015-05-14 |
United States Patent
Application |
20150129377 |
Kind Code |
A1 |
Hanna; Michael D. ; et
al. |
May 14, 2015 |
METHOD TO INCREASE CORROSION RESISTANCE IN FERRITIC NITROCARBURIZED
TREATED CAST IRON SUBSTRATES
Abstract
A method for improving corrosion resistance in FNC cast iron
substrates without the need for additional coating or painting. The
exemplary methods remove a portion of the FNC coating applied to a
cast iron substrate, preferably through polishing, to expose the
epsilon phase portion of the compound area. The epsilon phase
portion is thought to provide improved corrosion protection as
compared to non-polished FNC cast iron substrates. One exemplary
product that may be provided with improved corrosion protection
according to the above method is a brake rotor having a FNC
treatment.
Inventors: |
Hanna; Michael D.; (West
Bloomfield, MI) ; Holly; Michael L.; (St. Clair
Shores, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM Global Technology Operations LLC |
Detroit |
MI |
US |
|
|
Family ID: |
43822268 |
Appl. No.: |
14/601714 |
Filed: |
January 21, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12574940 |
Oct 7, 2009 |
|
|
|
14601714 |
|
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Current U.S.
Class: |
188/218XL ;
148/212 |
Current CPC
Class: |
C23C 8/32 20130101; F16D
65/127 20130101; C23C 8/80 20130101; F16D 2200/0013 20130101; F16D
65/125 20130101; F16D 69/027 20130101; F16D 2200/0017 20130101 |
Class at
Publication: |
188/218XL ;
148/212 |
International
Class: |
F16D 65/12 20060101
F16D065/12; C23C 8/32 20060101 C23C008/32; F16D 69/02 20060101
F16D069/02 |
Claims
1. A brake rotor comprising a ferritic nitrocarburized coating
extending from the outer surface of the brake rotor cheek.
2. A brake rotor as set forth in claim 1 wherein a portion of the
coating includes a diffusion layer, and a portion of the coating
including a compound layer.
3. A brake rotor as set forth in claim 2 wherein the compound layer
has a depth of between 10 and 20 microns.
4. A brake rotor as set forth in claim 2 wherein the compound layer
has a depth of about 15 microns, extending from an outer surface of
a brake rotor cheek.
5. A brake rotor as set forth in claim 2 wherein the diffusion
layer 30 includes an epsilon-Fe2-3(N,C) epsilon phase, a
gamma-prime Fe4(N,C) phase, and a ferrite phase.
6. A brake rotor as set forth in claim 1 wherein ferritic
nitrocarburized coating comprises a diffusion layer extending from
an outer surface of a brake rotor cheek, and a compound layer
underneath the diffusion layer, the compound having an inner
portion closer to the outer surface, and an outer surface portion
underneath the inner portion.
7. A method comprising ferritic nitrocarburizing a brake rotor
cheek to enhance surface hardness and corrosion resistance in the
brake rotor cheek.
8. A method as set forth in claim 7 wherein the ferritic
nitrocarburizing at a temperature ranging between about 525 and 650
degrees Celsius
9. A method as set forth in claim 7 wherein the ferritic
nitrocarburizing at a temperature of approximately 565 degrees
Celsius.
10. A method as set forth in claim 7 wherein the ferritic
nitrocarburizing is carried out to achieve a coating of about 10 to
20 microns.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 12/574,940 filed Oct. 7, 2009.
TECHNICAL FIELD
[0002] The field to which the disclosure generally relates to
methods for making ferritic nitrocarburized cast iron substrates
more corrosion resistant.
BACKGROUND
[0003] Motor vehicle disc brake systems utilize a disc brake rotor
at each respective wheel, wherein the disc brake rotor typically
includes a rotor hat for connecting to an axle hub of a rotatable
axle of the motor vehicle, and at least one annular rotor cheek
connected to the rotor hat, wherein the at least one rotor cheek
has a pair of mutually opposed braking surfaces onto which brake
pads are selectively applied when braking is desired.
[0004] Typically, brake rotors are either made solid or are
provided with internal ventilation. There are usually cast from
iron-based alloys and especially cast iron such as grey cast iron a
(G3000) and damped cast iron (G1800). Cast iron rotors are casted
to near shape and machined to shape after casting. The disadvantage
of cast iron rotors is that they exhibit insufficient corrosion
resistance compared to other conventional materials. Winter climate
and using the salt on roads can make the situation worse.
[0005] To remedy corrosion issues with cast iron rotors, a ferritic
nitrocarburizing (FNC) method to prevent the friction surface from
corrosion during operation has been developed. However, the
as-received FNC surface on non-frictional surface may still be
prone to corrosion after exposure to a humid atmosphere.
SUMMARY OF EXEMPLARY EMBODIMENTS OF THE INVENTION
[0006] The exemplary embodiments provide a method for improving
corrosion resistance in FNC cast iron substrates without the need
for additional coating or painting. The exemplary methods remove a
portion of the FNC coating applied to a cast iron substrate,
preferably through polishing, to expose the epsilon phase portion
of the compound area. The epsilon phase portion is thought to
provide improved corrosion protection as compared to non-polished
FNC cast iron substrates.
[0007] One exemplary product that may be provided with improved
corrosion protection according to the above method is a brake rotor
having a FNC treatment.
[0008] Other exemplary embodiments of the invention will become
apparent from the detailed description provided hereinafter. It
should be understood that the detailed description and specific
examples, while disclosing exemplary embodiments of the invention,
are intended for purposes of illustration only and are not intended
to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Exemplary embodiments of the invention will become more
fully understood from the detailed description and the accompanying
drawings, wherein:
[0010] FIG. 1 illustrates a perspective view of a brake rotor
according to one exemplary embodiment;
[0011] FIG. 2 is a section microscopic view illustrating the
ferritic nitrocarburized treatment applied to a portion of the
brake rotor as in FIG. 1; and
[0012] FIG. 3 is a section microscopic view of a portion of the
brake rotor of FIG. 2 with a portion of the ferritic
nitrocarburized treatment removed in accordance with an exemplary
embodiment.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0013] The following description of the embodiment(s) is merely
exemplary (illustrative) in nature and is in no way intended to
limit the invention, its application, or uses.
[0014] The exemplary embodiments provide a method for improving
corrosion resistance on cast iron substrates that include a
ferritic nitrocarburized (FNC) surface treatment. Two specific
exemplary products having FNC treated cast iron substrates include
solid and vented brake rotors.
[0015] Referring now to FIG. 1, a brake rotor 20 may be illustrated
according to one exemplary embodiment as having a hat portion 22
with a rotor cheek 24 extending about the periphery thereof. The
rotor cheek 24 may be generally referred to as a friction surface
of the rotor 20 that engages the caliper and other brake parts to
slow a vehicle during use, while the hat portion 22 may be
generally referred to as a non-frictional surface that does not
participate in the slowing of a vehicle through frictional
engagement and disengagement.
[0016] The shape of the brake rotor 20 as illustrated, and
specifically the respective shapes and relative dimensions of the
hat 22 and rotor cheek 24, are but one specific example of a
potentially infinite variety of possibilities or shapes and
dimensions of brake rotors and are thus not limited as illustrated
in FIG. 1.
[0017] The brake rotor 20 may be formed from an iron-based alloy or
steel, and especially cast iron such as grey cast iron a (G3000)
and damped cast iron (G1800).
[0018] A surface treatment 28 may be applied to the outer surface
26 of brake rotor 20 and provides the outer surface 26 with a
degree of friction resistance and with a degree of corrosion
resistance.
[0019] In the exemplary embodiment as shown in FIGS. 1 and 2, the
surface treatment 28 may be a ferritic nitrocarburized (FNC)
coating 28 applied to a depth of between 10 and 20 microns
extending from the outer surface 26, and more preferably about 15
microns. The ferritic nitrocarburizing surface treatment 28 may
enhance surface hardness and corrosion resistance in the brake
rotor 20, as well as providing increased friction for portions of
the rotor 20 that engage the caliper and other brake parts,
including the rotor cheek 24, to aid in slowing the vehicle to
which they are applied.
[0020] The process for applying the FNC surface treatment 28 may be
carried out at temperatures between about 525 and 650 degrees
Celsius (975 and 1200 degrees Fahrenheit); the preferred process
temperature may be approximately 565 degrees Celsius (1050 degrees
Fahrenheit) to achieve the desired coating of about 10 to 20
microns.
[0021] Upon application, as best shown in FIG. 2, a portion of the
FNC coating 28 may diffuse into the outer surface 26 of the brake
rotor 20 to form a diffusion layer 30, while the remaining portion
of the FNC coating 28 above the surface 26 may be referred to as
the compound layer 32. The compound layer 32, as stated above, may
preferably have a depth of between 10 and 20 microns, and more
preferably about 15 microns, extending from the outer surface
26.
[0022] The diffusion layer 30 may contain a mix of the phases,
including epsilon-Fe2-3(N,C) (the "epsilon phase" or "hexagonal
phase") and gamma-prime Fe4(N,C) (the "gamma phase") and a ferrite
phase that results from details of the process parameters such as
temperature, heat treatment time, and gas composition and pressure.
As shown in FIG. 2, the ferrite phase may become more predominant
further away from the compound layer 32 and outer surface 26.
[0023] The compound layer 32 may also contain a specific mix of the
phases, including the epsilon phase, the gamma phase, and a ferrite
phase that results from details of the process parameters such as
temperature, heat treatment time, and gas composition and
pressure.
[0024] The compound layer 32 may further be characterized as having
an inner portion 33 closer to the outer surface 26 of the hat 22
(and diffusion area 30), and an outer surface portion 34.
[0025] The inner portion 33 may be considered substantially in the
epsilon phase, also known as the dominant epsilon phase portion 33.
The outer surface portion 34 may contain a mix of the gamma phase,
epsilon phase as well as oxides such as Fe.sub.3O.sub.4.
[0026] Next, as best shown in FIG. 3, the hat 22, or other
non-frictional surfaces of the brake rotor 20 (not shown), may be
treated to remove the outer surface portion 34 and expose the
underlying inner portion 33 of the compound area 32. More
specifically, the treatment removes enough of the outer surface
portion 34 of the compound layer 32 to expose the dominant epsilon
phase portion 33 there within. In one exemplary embodiment, for a
surface treatment 28 in which the total compound layer 32 depth is
between about 10 and 20 microns, the treatment may remove about 2
and 6 microns of the outer surface portion 34 to expose the
interior portion 33.
[0027] The exposure to the epsilon phase portion 33 is believed to
provide improved corrosion resistance to the non-frictional
surfaces of the brake rotor 20 as compared with a non-polished
surface treatment (i.e. where the outer surface portion 34 remains
intact and may include primarily the gamma phase and oxides are
described above).
[0028] In one exemplary embodiment, the treatment may consist of
grinding, conditioning or polishing, preferably with a diamond
paste of 1 micron particles, of the outer coating surface 34 inward
to a depth of between about 2 and 6 microns to expose the dominant
epsilon phase 33 portion of the compound area 32. Experimental
testing of rotors 20 according to this treatment confirm that
samples having the exposed dominant epsilon phase portion 33 in the
hat 22 exhibited less corrosion compared to the rotors 20 in which
the outer coating 34 within the hat 22 remained unpolished.
[0029] While the above method for improving the corrosion
resistance was specifically discussed with respect to brake rotors
20 in the exemplary embodiments as described above, a similar
improvement in corrosion resistance may be expected in any cast
iron substrate in which an FNC surface treatment has been utilized.
Thus, the exemplary method for improving corrosion resistance may
be equally applicable to any FNC treated cast iron substrate.
[0030] The above description of embodiments of the invention is
merely exemplary in nature and, thus, variations thereof are not to
be regarded as a departure from the spirit and scope of the
invention.
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